Turbine wheel



Oct. 3, 1967 D. JOHNSON ETAL 3,345,035

TURBINE WHEEL Filed April 30, 1965 United States Patent O 3,345,035 TURBINE WHEEL Douglas Johnson and James H. Young, Indianapolis, Ind., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Apr. 30, 1965, Ser. No. 452,185 5 Claims. (Cl. 253-39) ABSTRACT OF THE DISCLOSURE `ingwave vibrations beyond the operating range of the wheel period.

Our invention relates generally to a turbine wheel and more specifically to a lightweight turbine wheel and its means of attachment within a turbine section. Since in the design of VTOL lift systems, the gas turbine lift engine operates only during the take-off and landing and comprises dead weight during cruise, the primary objective i-n the design of the lift engine is maximization of the thrust/ Weight ratio. Experience has shown that greater gains in the thrust/weight ratio can be had by reducing the weight rather than by improving the aerodynamics of the engine to increase the thrust. Because the turbine section of a gas turbine engine represents a lange percentage of the weight of the engine, it affords a correspondingly large opportunity for weight savings and consequently, gains in this area result in the greatest improvement in the thrust/weight ratio.

Accordingly, it is the object of this invention to generally reduce the weight of the turbine section of a lift engine and more specifically to provide the turbine section with a turbine wheel having the lightest possible weight while maintaining the structural integrity and simplicity.

This object and other objects and advantages will become more apparent from consideration of the following specification relating to the annexed drawing of a portion of a lift engine showing the turbine section provided with turbine wheels in accordance with the present invention.

Referring now to the drawing, the turbine section indicated generally at 12 comprises a casin-g 14 having spaced stiiener bands 16. The forward stiffener 16 carries an annular support 18 which has a cylindrical duct 20 mounted on its inner diameter. The duct 20V carries a pair of concentric annular members 22 and 24 which are radially spaced -to define a turbine inlet passage 26. Disposed radially inwardly of the cylindrical member 24 is a guide vane support 28. The downstream end of the support 28 is larger in diameter and has an inner shroud band 29 secured thereto by means of mating anges. The downstream portion of band 2-9 is contiguous with the end of member 24 and carries a plurality of guide vanes 30 which extend radially outwardly and span the annular passage 26.

Adjacent the downstream end of the duct 20 is an outer shroud band 32 for a second set of guide vanes 34. The outer shroud band 32 is secured to the casing 14 by hangers 36 which extend through the casing 14 to provide engine mounts 38. An inner shroud band is supported by the vanes 34 yand has a forward extension ICC 42 which forms the inner boundary for the turbine passage 44; the outer boundary of the turbine passage 44 being provided by the rearward portion of the duct 20. A bearing support sleeve 46 is mounted concentrically wit-hin the casing 14 by a double-walled diaphragm 48 secured at its outer circumference to the inner shroud band 40 adjacent the forward ends of vanes 34. An annular brace 50 is secured to the forward end of the forward extension 42 and to the middle of the diaphragm 48.

Just downstream of the first set of guide vanes 30 is a high pressure turbine indicated generally at 52. The high pressure turbine comprises a rotor wheel 54 having a rim 56 which is widened and has circumferentially spaced axial slots (not shown) to receive the roots of a number of radially extending turbine blades 58. The blades 58 have platforms 60 adjacent their inner ends which abut adjacent blade platforms to provide the inner boundary for the turbine passage 44 in the area of the blades. A forward ring 62 retains the blade roots in the slots in both the forward and rearward directions. A second rearward ring 64 acts as an air seal. The inner margin of the annular turbine wheel 54 has an arcuate annular snubber 66.

An annular forward integral extension 68 is provided on the wheel 54 adjacent the rim thereof. The extension 68 has a support 70 welded or otherwise suitably attached thereto. The support 70 and wheel 54 are in It-wo pieces for purposes of fabrication; it being understood that they could be machined in one integral piece. The support 70 is frusto-conical and has a hollow shaft 72 at its inner margin. The support 70 forms a substantially rigid and the sole support for the wheel 54. The

angle of the frusto-conical support 70 with respect to the shaft 72 isselected so that the axial deflection at its circumferential attachment due to centrifugal force balan-ces or partially balances theaxial deflection of :the rotor wheel at this point due to the pressure differential thereacross at design speed.

The shaft 72 extends forwardly to drive the compressor stage (not shown). A tie bolt 74 journaled in a bearing 71 mounted in the sleeve 46 carries the sleeve 72 between a forward shoulder and a spacer ring 76. The snubber 66 does not support the wheel 54 but acts somewhat like a pilot limiting its radial movement of the Wheel 54; the snubber 66 bottoming on the ring 76 when radial movement exceeds ay desired limit. Behind the spacer ring 76 is a sealing ring 78 havin-g spaced lands which form a labyrinth seal with insert 80 on bearing support 46. A snap ring '82 mounted in a groove in the end of support 46 holds insert 80. The inner race for the bearing 71 is clamped between the sealing ring 78 and a rear extension 84 threaded to the stub shaft 74. The extension 84 forms a seal with a labyrinth seal ring 86 carried by a power shaft 88 which is disposed concentrically within the stub shaft 74 and journaled in a second bearing 87 mounted in sleeve 46. The downstream end of the power shaft 88 has an integral support member 90. The support member 90 is double frusto-conical and carries an extension 92 on its outer circumference. The extension 92 is welded or otherwise suitably attached to the power turbine wheel 94 adjacent the rim 96. The outer rim 96 of the power turbine wheel 94 is widened and has a plurality of circumferentially spaced axial slots (not shown) in which are disposed the roots of a plurality of radially extending turbine blades 98. The turbine blades 98 have conventional platforms 100 adjacent their inner ends. A retaining ring 102 is shown to locate the roots within their slots. The tips of the power turbine blades 98 are connected by a shroud band 104. The outer circumferential wall of the shroud band 104 is ridged to form a labyrinth seal with the inner circumferential Wall of the exhaust duct 106 which is connected to a ange 107 on the downstream edge of the outer shroud band 32. The exhaust duct 106 carries a plurality of struts 108 which mount and center an exhaust cone 110 Within the exhaust duct 106 to form an annular jet nozzle 112.

The turbine wheel 54 is designed with the minimum possible thickness necessary to carry the radial stresses encountered during normal operation. This thinning of the wheel, however, introduces other limiting stress considerations caused by standing wave vibrations of the thinned turbine wheel 54. A troublesome type of Vibration which can occur is the lateral vibration of the rotating wheel which takes the form of standing waves at certain natural frequencies. These standing waves are characterized -by a plurality of radial nodes which have no axial movement while the remaining particles of the wheel move axially in a periodic back and forth motion. Visually, the movement of a cross section of the wheel would resemble that of a vibrating string. The natural frequencies at which the standing waves occur are a function of the thickness of the wheel; the natural frequencies decreasing with a decrease in wheel thickness. Thus the thinning of the wheel and the lowering of the natural frequencies introduces the danger of the natural frequencies of the wheel being included within the operating range of the turbine. However, the attachment of the driving cone or annular support 70 adjacent the rim 56 in effect places a circumferential node at the attachment circumference and increases the natural frequencies of the wheel -beyond the operating range of the turbine to thereby eliminate this danger.

This annular support or drive cone may take a conical form as in the high pressure turbine or a double conical form as in the low pressure turbine; the important feature being that the cone be able to carry the torque load produced by the -blades and that it be sufliciently stiff to eliminate the standing wave vibration deflections.

It should be understood, of course, that the above description is in connection with a preferred embodiment of the invention made for the purposes of disclosure only and that various modifications and changes may be made to the example chosen for disclosure without departing from the spirit and scope of the invention as defined in the appended claims.

We claim:

1. A lightweight turbine rotor for driving a rotatably mounted load bearing shaft and which is subject to standing wave vibration, comprising:

a rotor wheel having a thin web and a widened rim,

-blade mounting means in said rim,

a plurality of radially extending blades mounted in said mounting means,

means to provide a circumferential node at the outer circumference of said web, said means including an annular extension at the outer circumference of said web adjacent said rim, and

an annular support attached to said extension and to said shaft to constitute the sole axial and radial support for said rotor wheel whereby said rotor wheel is adapted to drive said shaft through said web, annular extension and annular support.

2. The combination as claimed in claim 1 wherein said annular support is frusto-conical in cross section.

3. The combination as claimed in 2 wherein the angle of said cone is chosen so that the axial deflection thereof at its greater diameter due to centrifugal forces balances the axial deflection of the rotor wheel due to air loading of said blades at design speed.

4. The combination as claimed in claim 1 wherein said annular support is double frusto-conical in cross section.

5. The combination as claimed in claim.4 wherein the angles of said inner and outer cones are chosen so that the axial deflection thereof at its greatest diameter due to centrifugal forces balances the axial detiection of the rotor wheel due to air loading of said blades at design speed.

References Cited UNITED STATES PATENTS 1,711,631 6/1955 Willgoos 253-39 X 2,738,126 3/1956 Edwards 253-39 X 2,749,026 6/1956 Hasbrouck et al. 253-39 X 2,922,618 1/1960 Paulson 253-39 3,135,562 6/1964 Davies et al 253-39 X 3,163,353 12/1964 Petrie 253-39 X 3,249,293 5/1966 Kotf 253-39 X FOREIGN PATENTS 810,652 3/ 1959 Great Britain.

MARTIN P. SCHWADRON, Primary Examiner.

-EVERETTE A. POWELL, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,345,035 October 3, 1967 Douglas Johnson et a1.

It is hereby certified that error appears n the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

i Column 2, line 36, after "attachment" insert point llne 37, for "theaxal" read the axial column 4, line 34,

for "1,711,631" read 2,711,631

Signed and sealed this 1st day of October 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. A LIGHTWEIGHT TURBINE ROTOR FOR DRIVING A ROTATABLY MOUNTED LOAD BEARING SHAFT AND WHICH IS SUBJECT TO STANDING WAVE VIBRATION, COMPRISING: A ROTOR WHEEL HAVING A THIN WEB AND A WIDENED RIM, BLADE MOUNTING MEANS IN SAID RIM, A PLURALITY OF RADIALLY EXTENDING BLADES MOUNTED IN SAID MOUNTING MEANS, MEANS TO PROVIDE A CIRCUMFERENTIAL NODE AT THE OUTER CIRCUMFERENCE OF SAID WEB, SAID MEANS INCLUDING AN ANNULAR EXTENSION AT THE OUTER CIRCUMFERENCE OF SAID WEB ADJACENT SAID RIM, AND AN ANNULAR SUPPORT ATTACHED TO SAID EXTENSION AND TO SAID SHAFT TO CONSTITUTE THE SOLE AXIAL AND RADIAL SUPPORT FOR SAID ROTOR WHEEL WHEREBY SAID ROTOR WHEEL IS ADAPTED TO DRIVE SAID SHAFT THROUGH SAID WEB, ANNULAR EXTENSION AND ANNULAR SUPPORT. 